International projectionist (Nov-Dec 1933)

December 1933 INTERNATIONAL PROJECTIONIST 27 Amperex Shows Two New Sound Tube Types AMPEREX Electronic Products has introduced two new sound picture tube types that are winning favor in the field — the Amperex 205-D, new in every respect, and the greatly improved Amperex 264-B. The demands made on the 205-D are by far more severe than that of any other similar tube. The same tube is expected to operate asa rectifier (as was the custom, in 1920), as an amplifier, and as an oscillator. The plate dissipation in this tube is also respectively higher than in other tubes. To overcome all these difficulties, Amperex set about designing a tube with the following characteristics: 1. Long Life — It is neither feasible nor economical to have tubes fail during performance. Definite life expectancy should be assured. 2. Uniform Characteristics — All 205D tubes used as amplifiers in motion picture sound equipment are in push-pull circuits, which requires that they be carefully matched. 3. No Output Hum — In some sound equipments the 205-D is followed by a high-gain amplifier, so that any variation in filament temperature (filament is invariably A. C. -operated) would be noticeable in the output. 4. No Arcing Between Electrodes — High insulation should exist between electrodes, so that even at the highest potentials no arcing will occur. 5. High Efficiency — The large effective plate area and the efficient filament insure high mutual conductance. 6. Fast Pick-up and Constant Uniform Speed in Control Boxes — Automatically operated change-over equipments depend upon the efficient operation of the 205-D. 7. Rigidity in Construction — Continuous vibration in projection rooms, daily handling for test purposes, as well as unavoidable shipment of single tubes, necessitates a construction which will not permit dislocation of the electrodes with respect to each other. Greatly Improved 205-D In the new Amperex 205-D long life has been insured by the use of a special alloy filament, carefully coated and properly life-tested before its final adaptation. The important characteristics of this new tube will not substantially vary even at extremely varied voltages encountered. The relatively small quantities of 205-D's used permit manufacture and test of them under laboratory conditions. The material for the electrodes is subjected to chemical tests before use and special equipment has been designed to insure proper alignment of the various electrodes. To overcome the arcing between the electrodes, the high-voltage plate lead has not been incorporated in the press as is usually the custom, but is placed at a distance of almost a half inch from the grid lead in the side of the flare. NOTES from the SUPPLY FIELD Special precaution has been taken (by placing deflectors on the press), so that no metallic vapors could deposit between the elements. The filament has been so arranged within the structure that the entire plate area is effective. The same factors which insure long life, automatically give optimum efficiency. One hundred percent of the filament area is emitting, so that there is very little change in the electrical characteristic of the tube from a relatively low to a relatively high filament voltage. Fast pickup as well as constant uniform speed during operation, which is entirely dependent on uniformity of electrical characteristics and holding closely to a standard characteristic, is insured by dynamic as well as static tests. Rigid structure is assured by using a four-point support. The Amperex 264-B The other improved tube type is the Amperex 264-B, the characteristic use of which has imposed certain demands of which the most important is absolute freedom from noise. A constant source of great annoyance with this type tube has been the corrosion occurring at the point of contact of the tube socket with the base prong, resulting in noise. It has been found that this difficulty could be overcome by plating the tube prongs with a semi-noble metal that will prevent corrosion. The Amperex 264-B retains all the characteristics of the 264-A type, particularly the low microphonic response, and has in addition the silver plated prongs to give additional assurance that it will not become noisy from corrosion during operation. Obviously, this new 264-B tube is fully interchangeable with the older type 264-A tube. Both these new tube types are now available in unrestricted quantities. SYNCROFILM CARBON SAVER THE Syncrofilm Carbon Saver developed by the Weber Machine Corp., makers of the well-known sound reproducing system of the same name, is now ready for distribution in the projection field. This Saver, reports the Weber company, is not a gadget but an accurately machined equipment which has been designed by practical projectionists. The Saver is easy to operate, and results in no fuss or dirt. The complete Syncrofilm Saver outfit consists of 1 frame for drills, 3 positive and 2 negative adapter rods, 2 drills with handles, 12 extra points for adapters, 1 dust cup, and 1 bushing for drilling the negative carbon. Price for the complete outfit is $20. The manufacturer is located at 59 Rutter St., Rochester, N. Y. L. U. 640 ELECTIONS Officers elected at the last meeting of LA. Local 640 (Nassau and Suffolk counties, L. I., N. Y.) are: Joseph Engle, pres. ; M. D. O'Brien, v. p. ; Rodney Titcomb, rec. sec; Dave Peshkin, fin. sec; and Frank Cummings. b.a. Banish your 205 tube worries. Install the new DUOVAC 205-D tube and enjoy perfect sound and absolute security. The 205-D with the new carbon anode development. — Adv. THE CAESIUM— OXYGEN— SILVER PHOTOELECTRIC CELL M. /. Kelly MEMBER, TECHNICAL STAFF, BELL TELEPHONE LABORATORIES D1 lURING the past three years the photoelectric cells of the potassiumhydride-cathode type have been replaced by cells employing a new and more highly efficient cathode. This cathode has a core or base of pure silver upon which is formed a matrix of caesium oxide, silver oxide, and finely divided silver. This matrix is covered by an absorbed layer of caesium of atomic dimensions and in eauilibrium with a small amount of strongly absorbed free caesium in the matrix. With an incandescent lamp as a light source, as is used in sound-picture and picture transmission systems, this cathode is more than fifty times as sensitive as is the potassium-hydride-cathode